Beryllium hydride

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Beryllium hydride
Identifiers
CAS number [7787-52-2]
Properties
Molecular formula BeH2
Molar mass 11.03 g mol−1
Appearance amorphous white solid[1]
Density 0.62-0.65 g cm−3, solid[2]
Melting point

250 °C with decomp.[1]
Related compounds
Other cations lithium hydride, calcium hydride, boron hydrides
Related compounds beryllium fluoride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Beryllium hydride, BeH2, is a chemical compound of beryllium and hydrogen. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded.[1]

[edit] Synthesis

BeH2 was first synthesised in 1951 by reacting dimethylberyllium, Be(CH3)2, with lithium aluminium hydride, LiAlH4[3].

Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C(CH3)3)2 at 210 °C[4].

The purest beryllium hydride is obtained by the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2[1]:

Be(BH4)2 + 2PPh3 → 2Ph3PBH3 + BeH2

[edit] Structure

BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g cm−3) was reported[2], prepared by heating amorphous BeH2 under pressure, with 0.5-2.5% LiH as a catalyst.

A more recent investigation found that crystalline beryllium hydride has a body-centred orthorhombic unit cell, containing a network of corner-sharing BeH4 tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH2[5].

[edit] References

  1. ^ a b c d Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. , p. 115
  2. ^ a b G. J. Brendel, E. M. Marlett, and L. M. Niebylski (1978). "Crystalline beryllium hydride". Inorg. Chem. 17 (12): 3589–3592. doi:10.1021/ic50190a051. 
  3. ^ Glenn D. Barbaras, Clyde Dillard, A. E. Finholt, Thomas Wartik, K. E. Wilzbach, and H. I. Schlesinger (1951). "The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride". J. Am. Chem. Soc. 73 (10): 4585–4590. doi:10.1021/ja01154a025. 
  4. ^ G. E. Coates and F. Glockling (1954). "Di-tert.-butylberyllium and beryllium hydride". J. Chem. Soc.: 2526–2529. doi:10.1039/JR9540002526. 
  5. ^ Gordon S. Smith, Quintin C. Johnson, Deane K. Smith, D. E. Cox, Robert L. Snyder, Rong-Sheng Zhou and Allan Zalkin (1988). "The crystal and molecular structure of beryllium hydride". Solid State Communications 67 (5): 491–494. doi:10.1016/0038-1098(84)90168-6. 
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